The charged particle beam device represented by the scanning electron microscope scans finely converged charged particle beams on a sample to attain desired information from the sample (for example, sample images). This sort of charged particle beam device is used in most cases for the evaluation of semiconductor devices or the analysis of the defectives thereof. The trend of microstructure and multi-layered structure in the semiconductor devices advances year by year, and in order to analyze the defectives of multi-layered devices, a method of evaluating a device by using a thin film thereof has become important. A transmission signal transmitted through the sample is generally used for observing a thin film sample. Since the transmission signal (dark field signal) scattered within and transmitted through the sample significantly reflects the atomic number contrast of the sample, it is known to be effective for analyzing the defectives of a device.
The conventional method of detecting transmitted signal particles will be described with reference to FIG. 5 and FIG. 6. As shown in FIG. 5, in the charged particle beam device that incorporates a sample stage to observe a large sample, a sample stage 160 is disposed below an objective lens 20, and a thin film sample 14 is mounted on this stage. Signal particles (18a, 18b) transmitted through the thin film sample 14 pass through a through hole 161 which is bored in the sample stage 160 for the transmitted signal particles, and are detected by a transmitted signal detector 17 furnished below the sample stage. Here, among the transmitted signal particles, only the signal particles 18a having passed through the through hole 161 are detected by the transmitted signal detector 17. And, an aperture 19 is provided between the sample stage 160 and the transmitted signal detector 17, to restrict the scattering angles of the signal particles 18a detected by the transmitted signal detector 17. On the other hand, the magnetic field generated by the objective lens 20 to focus the primary beams, is formed on the upper area (toward the source of charged particles) viewed from the bottom of the objective lens. Therefore, secondary signal particles 11 emitted from the surface of the sample 14 are attracted to an electrostatic field 130 generated by a secondary signal detector 13 provided below the objective lens, and are detected by the secondary signal detector 13.
Further, the non-patent document 1 (“A STEM image observation utilizing secondary electron detector”, reports of the Japanese Medical SEM Symposium, vol. 11, 15-16 (1982)) discloses the following method of obtaining the transmitted signal image of the sample 14. As shown in FIG. 6, the method uses a sample mount 150 with a metal part covering an area under the thin film sample 14. The secondary signal detector 13 disposed below the objective lens detects secondary signal particles 12 emitted by collision of the transmitted signal particles (18a, 18b) against the metal part under the sample, thus obtaining the transmitted signal image of the sample 14. Also in this case, since the focusing magnetic field by the objective lens is generated on the upper area (toward the source of charged particles) viewed from the bottom of the objective lens, the secondary signal particles 11 emitted from the surface of the sample 14 are attracted to the electrostatic field 130 generated by the secondary signal detector 13 below the objective lens, and are detected by the secondary signal detector 13.